This application claims the benefit of U.S. Provisional Application Serial. No. 60/174,955 titled xe2x80x9cMethod for Rapid Noise Reduction from an Asymmetric Digital Subscriber Line Modem,xe2x80x9d naming the same inventors, filed on Jan. 7, 2000, claiming priority benefits under 35 U.S.C. xc2xa7119(e).
The present invention relates to communications in digital subscriber lines. More specifically, it relates to a method for rapid noise reduction from a splitterless asymmetric digital subscriber line modem.
Digital Subscriber Line (xe2x80x9cDSLxe2x80x9d) is a developing modem technology that allows existing copper telephone lines to carry high bandwidth information. Familiar twisted-pair telephone lines are then able to carry high speed data communication to and from a customer site in addition to retaining a plain old telephone service (xe2x80x9cPOTSxe2x80x9d) channel for voice communication. At the customer site, a DSL modem receives the downstream signal representing data for a customer from a central office for a telephone company and transmits an upstream signal representing data from the customer to the central office.
One configuration of DSL is generally termed Asymmetric Digital Subscriber Line (xe2x80x9cADSLxe2x80x9d). ADSL allows high-speed data transport to the customer site but only medium-speed data transfer from the customer site, whence the asymmetry. ADSL also allows the simultaneous use of the ADSL modem and POTS on the same telephone line. In this configuration, at a point where the twisted-pair telephone line enters the customer site, filters split the POTS channel from the ADSL modem channels. One problem with this type of ADSL, however, is that a technician from the telephone company has to visit the customer site and install the splitter, referred to as xe2x80x9cthe truck roll.xe2x80x9d
To overcome this problem, another configuration of ADSL forgoes the requirement of a splitter at the customer site. This configuration is generally called xe2x80x9csplitterless ADSLxe2x80x9d and also goes under the name of xe2x80x9cG.Lite.xe2x80x9d Splitterless ADSL is described in the International Telecommunications Union-Telecommunication Standardization Sector (hereinafter xe2x80x9cITU-Txe2x80x9d, formerly known as the CCITT) Recommendation G.992.2, February 1999, which is incorporated herein by reference. ITU-T standards can be found on the World Wide Web at the Universal Resource Locator (xe2x80x9cURLxe2x80x9d) xe2x80x9cwww.itu.ch.xe2x80x9d Splitterless ADSL modems include those manufactured by 3Com Corporation of Santa Clara, Calif., Lucent Technologies of Murray Hill, N.J., Texas Instruments of Dallas, Tex., and others.
In splitterless ADSL, an ADSL modem directly shares the same twisted-pair telephone line as a POTS telephone without the intervention of a splitter. Sharing the same twisted-pair telephone line, however, may result in some of the upstream ADSL signal bleeding over into the audible frequency range of the POTS telephone. Audible noise effects, such as a buzzing in the earpiece or speaker, are heard on the POTS telephone when off-hook. Also, sharing the same twisted-pair telephone line may introduce noise into the downstream data transfer. The downstream noise effect is the response of the internal circuitry of the telephone to the upstream ADSL signal. Both types of noise may impair the simultaneous use of the telephone and the ADSL modem.
Each telephone has a different response to the upstream ADSL signal: some telephones introduce little audio or downstream noise, such as many of the cordless telephones, while other telephones introduce a lot of either noise, thus severely reducing the customer""s simultaneous use of the telephone and the rate at which the modem can receive data. Therefore, a method for reducing the audible and downstream noise should preferably respond to whether the telephone introduces a little or a lot of noise.
It is desirable, therefore, to reduce the downstream noise introduced by the telephone to reduce audible noise in the telephone and optimize the downstream data transfer. It is also desirable to achieve noise reduction for a wide range of telephone models. This may allow customers to use their telephones while the ADSL modem is transferring data.
In accordance with preferred embodiments of the present invention, some of the problems associated with rapidly reducing noise in a splitterless ADSL modem are overcome.
One aspect of the invention includes a method for rapidly reducing noise from a telephone in a splitterless ADSL modem to enable simultaneous use of the telephone and the modem. The telephone and the modem share a telephone loop. The method includes measuring a selection of transmission characteristics for the telephone loop. The modem determines whether a table entry is associated with the selection of transmission characteristics. The table entry comprises stored transmission characteristics that permit the modem to achieve a data transfer mode. When the table entry is associated with the selection of transmission characteristics, the modem retrieves a power level from the table entry and configures the modem to transmit at the power level. In this manner, the modem may recognize characteristics of the telephone loop and adopt a configuration of its upstream transmitter that had previously successfully allowed the modem to attain a data transfer mode.